1. Field of the Invention
The present invention relates to a reactor for polycrystalline silicon used in producing polycrystalline silicon according to the Siemens method, and relates to a polycrystalline silicon production method.
2. Description of Related Art
The Siemens method is known as a method for producing polycrystalline silicon of high purity used as a material of semiconductors. In the Siemens method, a raw material gas composed of chlorosilane and hydrogen is brought into contact with a heated silicon seed rod to deposit polycrystalline silicon on the surface through reactions of the raw material gas. A reactor for polycrystalline silicon in which many silicon seed rods are installed upright in a reactor is used as an apparatus for carrying out this production method. In general, the silicon seed rod is formed in a n-shape, with upper ends being coupled, and both lower ends thereof are fixed to an electrode mounted on the bottom of the reactor.
Then, electricity is supplied through the electrode located on both ends to a whole part of the silicon seed rod, thereby heating the silicon seed rod in its entirety by Joule heat thereof to a temperature at which the raw material gas is thermally decomposed (for example, from about 1050° C. to 1100° C.). The raw material gas supplied into the reactor is in contact with the surface of the heated silicon seed rod to cause thermal decomposition or hydrogen reduction, thereby polycrystalline silicon is deposited on the surface of the silicon seed rod. This reaction proceeds continuously, by which polycrystalline silicon grows in a column-shape (refer to Japanese Patent No. 2867306, for example).
Into the reactor for polycrystalline silicon, a raw material gas is in general supplied from the bottom of the reactor. The raw material gas is supplied from a raw material gas supply port installed at the bottom of the reactor so as to be uniformly dispersed to all silicon seed rods in the reactor.
Incidentally, when a raw material gas is directly blown toward the lower part of the column-shaped polycrystalline silicon heated by supply of electricity, the temperature of the lower part decreased compared to that of the other part, thereby the speed for growing polycrystalline silicon deposited on the surface of the column-shaped polycrystalline silicon is decreased. As a result, the lower part of the column-shaped polycrystalline silicon may be partially recessed to result in undesirable morphology. Further, the raw material gas is not sufficiently supplied and stagnates at the upper part of the column-shaped polycrystalline silicon. Thus, popcorn-like irregularities may be developed on the surface of silicon to result in undesirable morphology. When the undesirable morphology is generated, polycrystalline silicon may be deteriorated in quality to result in a lower yield.
The present invention has been made in view of the above situation, an object of which is to provide a reactor for polycrystalline silicon capable of supplying stably a raw material gas to the surface of a silicon seed rod and preventing the undesirable morphology of polycrystalline silicon.